Before you are two balls, one solid and one hollow. They are to all appearences completely identical: same size, same weight, same outer material (though one might assume, correctly, that the hollow ball would need a higher-density material on the inside to make it the same weight).

Without breaking either of the balls, how can you easily determine which is hollow?

Assume that the material is solid enough that a hitting the side of the hollow ball will not result in any noticeable echo or vibrations.

"Assume that the material is solid enough that hitting the side of the hollow ball will not result in any noticeable echo or vibrations".

Is an unfortunate phrase. First of all, what does "solid enough" mean?. And secondly, all solids transmit vibrations.

Being a solid means keeping your atoms in the same equilibrium position with respect to each other. That being said, oscilations from this equilibrium position (vibrations) are done by all solids in nature.

Maybe next time you ask this problem, you should say something like "Without breaking either of the balls, or performing any kind of internal scan, how can you determine which is hollow?".

Other than that, this is a very nice problem. I'm rating it with a 5.

Edited on March 26, 2005, 4:00 pm

Posted by ajosin on 2005-03-26 15:45:16